Lisbeth Darsh used to own a CrossFit affiliate in Watertown, Connecticut, and also worked for CrossFit Inc. for six years. In that time, she says, she only saw people leave a workout to throw up “a handful of times.”

Now a writer, editor, and social media consultant in Scotts Valley, California, Darsh still goes to CrossFit classes regularly. “I, personally, have never thrown up from a CrossFit workout,” she says. “I’ve come close, but I have a strong stomach. I didn’t even throw up when I rode in a fighter jet.”

CrossFit is not the only mega-hard workout that’s become popular in recent years. For fitness video series P90X and Insanity, as well as obstacle course races like Tough Mudder (where obstacles sometimes involve fire or live electrical wires), being difficult is a selling point.

“Tough times don’t last, tough people do!... Pain is temporary,” reads a t-shirt prominently displayed on the Tough Mudder website. Vomit or no vomit, the experience will be unpleasant, but you will be better for it. This is the promise of extreme exercise.

But to determine why people are attracted to exercise programs where vomiting or being shocked by a live wire seem to be at least somewhat more likely than in day-to-day life, we must first ask: Why exercise at all?

The reasons people exercise can’t be boiled down to dichotomies: Either they like working out or they don’t, they’re motivated or they’re not. The truth is that motivation is complex, and some reasons for working out are healthier than others.

Philip Wilson, an associate professor in the department of kinesiology at Brock University in Canada, has been studying exercise motivation for the past 10 years. He says that while intrinsic motivation—exercising because you think it’s fun, and you actively want to do it—is the ideal for creating a long-term habit, ultimately exercise can’t make you love it if you don’t.

In the absence of a genuine love for running on the elliptical, exercising because you know it’s good for you, or because you want to be the type of person who exercises, are better motivations (in terms of feeling good and sticking with it) than exercising because you’d feel bad about yourself if you didn’t, or because you think someone else wants you to.

Wilson says it could be that people who are attracted to intense exercise programs are intrinsically or autonomously motivated, that they are looking to prove themselves at a new challenge, and they enjoy the hard work these programs involve. (They may also like exercise itself less than “having exercised”—one 2007 study found that participants felt tense and distressed during their workout, but felt better once it was over.)

“These CrossFit programs do not draw couch potatoes,” Wilson says.

That certainly seems to be the case for Darsh.

“[CrossFit] was a way to throw myself into yet another sport that demanded a lot of me, [where] I really had to bear down and go to a different place in order to get where I wanted to go,” she says. “I’d found that in cycling and in triathlons, and then moved on to CrossFit.”

But Wilson says it’s also possible that some of the more troubling motivations are behind the trend—that people are seeking a reward (such as losing weight), “or they have a very fragile sense of self-worth.” Unhealthy motives are more likely, according to Wilson, when people take extreme exercise to, well, its extreme—pushing through intense pain, or continuing to work out through nausea.

Nausea is a warning sign, says Anthony Wall, director of professional education at the American Council on Exercise. There are a few things that can cause nausea during a workout. One is a full stomach, which isn’t much of a cause for worry. (Just maybe next time, do your daily P90X video before entering a hot dog eating contest, not after.) Another is dehydration, when an imbalance of the body’s electrolytes can cause vomiting.

The risk for vomiting from extreme exercise, specifically, comes from working so intensely that the body can’t get enough oxygen to fuel its muscles, leading to a build-up of the waste product lactate.

“When you’re working at a lower intensity, you’re able to produce energy and get rid of the waste,” Wall explains. “As your intensity increases, your ability to get rid of that waste, or reuse it within the body, becomes compromised and that’s what makes you start to feel sick. It’s a buildup of waste products within the body.”

Nausea can also, in rarer cases, be a symptom of rhabdomyolysis—in which damaged muscles break down, and their protein enters the bloodstream. There have been a few cases of people coming down with the condition after a CrossFit workout, and “Uncle Rhabdo,” another cartoon clown, even more alarming than Pukie, illustrates the danger.

Surely, most people aren’t going out of their way to meet Pukie or Rhabdo, though Darsh notes that “some people wear [throwing up] as a badge of pride, some people avoid it.”

She explains, though, that there is an appeal to pushing yourself as hard as you can. “You’re looking to find the edge, and you never really know where the edge of yourself is unless you go over it,” she says. “That’s something I think we search for a lot in life. All of life is not a happy walk in the park, and maybe there’s a corollary there for some of us in our workouts. By finding this point that we push past in our workouts, it helps us to carry on in a similar fashion in our personal lives.”

There is some evidence that people are drawn to hard work when life gets overwhelming. A recent study published in the Journal of Consumer Research found that people prefer products that require them to work hard when they feel low in control. In the study, feeling out of control with respect to their health especially drew people to exercise, but lead study author Keisha Cutright says feeling generally out of control could still make intense workouts seem appealing.

“One piece of the story may be that exercise is the one thing that you can control in your life, when the economy is down, when things aren’t going so great with your job or in your dating life,” says Cutright, an assistant professor of marketing at the University of Pennsylvania. “Particularly with exercising, we believe that the more we put into it, the more we’ll get out of it… Pretty much everything else we do in life, someone else has some influence. And this is something where you feel like you’re in charge.”

And super-athletic fitness nuts like the ones often drawn to CrossFit or Tough Mudder probably do feel like exercise is something they can control, that they understand and exceed at.

“I think there are some people who are very driven by pushing their limits,” Wilson says. “And yet there are still a lot of people who believe that in order for exercise to be good for you, it has to hurt, and it’s completely not true.”

For the record, the American Council on Exercise does not advocate working out so hard that you feel nauseous.

While some CrossFit enthusiasts have disavowed Pukie, saying he casts the sport in a negative light, Darsh doesn’t mind him. She wrote a blog post in 2013 called “In Praise of the Vomiting Clown.”

“The clown is…he’s there,” she says. “He’s just a reminder that shit happens. And that you have to keep going. Maybe he’s more of a cavalier way to give that message… I don’t think it’s dissimilar to what Springsteen sang about years ago: ‘I wanna go out tonight, I want to find out what I got.’”

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Julie Beck is a senior editor at The Atlantic, where she covers family and education.